Compress images online
Reduce the file size of JPG, PNG and WebP images without visibly losing quality. Compression runs entirely in your browser, so your photos are never uploaded anywhere.
100% private: files are processed in your browser and never uploaded to any server.
How it works
- Drop one or more images into the box above, or click to choose files.
- Pick a quality level, or type an exact target size in KB.
- Download each compressed image — the size saving is shown next to every file.
What actually happens when an image is compressed
A JPEG is not a grid of pixels the way a screenshot is. The encoder chops the picture into eight-by-eight blocks, describes each block as a sum of wave patterns, and then throws away the patterns your eye is worst at noticing — fine, high-frequency detail, and colour information more aggressively than brightness. The quality setting is really a dial on how much gets discarded. That is why compression is called lossy: the bytes you save are detail that does not come back.
This also explains why some images shrink far more than others at the same setting. A portrait against a plain wall is mostly smooth gradients, which those wave patterns describe very efficiently. A photo of gravel, foliage or a crowd is high-frequency almost everywhere, so the encoder has to keep much more to avoid visible mush. Two files of identical dimensions can easily differ fourfold in size after compression purely because of what is in them.
Quality slider or exact target size
There are two honest ways to compress, and they answer different questions. Setting a quality level answers "how good should this look?" and lets the file size land wherever it lands — the right approach when you are optimising a website and care about appearance more than a specific number. Setting a target size answers "what will the upload form accept?" and lets quality land wherever it must.
This tool does both. When you give it a target in KB, it does not simply guess a quality value: it encodes repeatedly, narrowing in on the highest quality that still fits under your limit, and only starts reducing the pixel dimensions when quality alone cannot get there. That order matters. Crushing quality while keeping every pixel is what produces the blocky, smeared look people associate with over-compressed images; shedding pixels first almost always looks better at a hard limit.
Compressing without uploading anything
Compression is the single most common reason people hand a private image to a random website. The scenario repeats endlessly: a form demands a photo under some size, the phone produces a four-megabyte file, and the fastest way out is the first search result — which uploads a passport scan or a payslip to a server nobody can inspect.
Imgnest does the encoding in your browser, using the same codecs your device already ships. The file is read from disk by the page, re-encoded in memory, and written back out as a download. Nothing is transmitted, so there is no copy on anyone's server, no retention policy to trust and no queue to wait in. Load the page, disconnect from the internet, and compression still works — which is the only proof of a privacy claim that actually means anything.
Good to know
File size comes from two things multiplied together: how many pixels there are, and how many bytes are spent on each. Most people only touch the second. If you need a big reduction, reducing the dimensions first and then compressing at a sane quality looks far better than crushing a 4000-pixel photo with the quality slider alone.
As a rule of thumb, JPEG quality below about 60% starts to be visible and below 40% is obvious. If you set a target size in KB, this tool searches for the highest quality that fits and only scales the image down when quality alone cannot get there.
PNG behaves differently: it is lossless, so it cannot discard detail to save space. A photographic PNG will barely shrink — convert it to JPG first if the destination allows it. Whatever happens, the result is never handed back larger than the file you started with.
Read more: How to compress an image to an exact size in KB · HEIC vs JPG: why your iPhone photos won't open · PNG vs JPG vs WebP: which one should you use? · Why in-browser image processing is more private
Frequently asked questions
Does compressing an image reduce its quality?
Lossy compression removes detail the eye barely notices. At the default setting the difference is invisible for most photos; if you need a smaller file you can lower the quality or set a target size and let the tool find the best balance.
Are my images uploaded to a server?
No. Imgnest compresses images with code that runs inside your browser. Your files never leave your device — you can even disconnect from the internet after the page loads and the tool keeps working.
Is there a limit on file size or number of images?
No. Because processing happens on your device, there are no queues, no daily limits and no maximum file size beyond what your browser can handle.
Which formats can I compress?
JPG/JPEG, PNG and WebP. If you need to shrink an iPhone photo, use the HEIC to JPG converter first, then compress the result.
Is any image data sent to a server?
No. Compression runs entirely in your browser using built-in and WebAssembly encoders. Your file never leaves the device, which you can verify by going offline after the page has loaded.
Why is my compressed file sometimes larger than the original?
It can happen when the original was already heavily optimised, or when a PNG with few colours is re-encoded as a JPEG. When that happens the tool keeps the smaller original instead of handing you a bigger file.